Method of and apparatus for automatically charging accumulator batteries



Jan- 19, 1954 J. P. GUELPA 2,666,883

METHOD OF' AND APPARATUS FOR AUTOMATICALLY CHARGING ACCUMULATORBATTERIES Filed Sept 6, 2 Sheets-Sheet 1 L r F2 l/T'J 1 l rib' 1 ng. 2

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METHOD OF AND APPARATUS FOR AUTOMATICALLY CHARGING AccuMULAToR BATTERIESFiled Sept. 6. 1950 v2'Sheets'-Sluaa1f 2 T Flg- J *By MMV-M PatentedJan. 19, 1954 METHOD OF AND APPARATUS FOR AUTO- MATICALLY CHARGINGACCUMULATOR BATTERIES Jean Pierre Guelpa, Colombes, France, assignor toCompagnie Generale dElectricite, Paris, France, a corporation of FranceApplication September 6, 1950, Serial No. 183,338

The most rational charging system is there fore that which comprises afirst constant-cur-r rent stage employing the full maximum lpower of thecharging station, followed, immediately the evolution of gas commences,by a progressive reduction of the charging current.

Various systems have been proposed along these lines. In one suchsystem, it was suggested that the actual evolution of the gas shouldcontrol the charging source. It has also been proposed to employ eitherthe increase in the voltage charge in the battery or the state of chargeof the battery, as measured by an amperehour meter.

Apart from the fact that certain defects arise in the practicalapplication of these two methods, they presuppose that the evolution ofgas takes place at a certain voltage or at a certain state of charge ofthe battery, which is only correct as a first approximation. Theinfluence of temperature, of the strength of the charging current and ofthe ageing of the battery modify the phenomena and cause in certaincases either overcharging prejudicial to the good preservation of thebattery components or incomplete charging in the time available.

According to the present invention there is provided a method ofautomatically charging an accumulator battery in two stages, the rststage being at constant current and the second stage at variablecurrent, the rst stage comprising the step of charging the battery froma constant current charging source until the temperature dilerence Tbetween the interior of the battery and the ambient air is more than thetemperature diiierence Te which isset up when the fully-charged batteryis overcharged at the nalrate of charging, and said second stagecomprising the steps of reducing the charging current until thetemperature difference T does not exceed Te and maintaining thistemperature difference until the battery is fully charged,

8 Claims. (Cl. S20-23) Calculation and experiment show that forgenerally acceptable initial currents of the order of 0.20 I (I beingthe capacity in ampere-hours of a battery discharged in five hours) andas long as no gassing occurs the temperature increase is extremelysmall. For a battery of normal construction (starting or traction) whichis completely heat-insulated, it is of the order of 1 C. per hour.mences, the internal resistance increases and the electrolysis of thewater brings about an additional evolution of heat. At the end of thecharging operation, the equivalent in energy ci the difference betweenthe theoretical and true voltages of the electrolysis of the water (1.1v. and 2.6 v. approximately) completely takes the form oi' heat, theevolution of which is then much greater. The same current of 0.20 Iwould produce an hourly temperature increase about ten times higher witha heat-insulated battery assumed to be completely charged.

In fact, batteries are not heat-insulated and radiate differingquantities of heat according to their construction and their differencein ternperature from the ambient air. However, the ratio between the twotemperature increases tends to be proportional to the internal evolutionof heat. Thus, in the preceding example, the ratio will still be tentimes higher in the second case than in the rst.

The current which, when applied to a completely charged battery producesan evolution of heat equal to that in the rst case is about 0.035 I. Itis to be remarked that this figure is that which is given by mostauthors for the equalisation current considered to be noninjurious tobatteries.

The charging method deiined will therefore be as follows:

When the accepted iinal rate of charge has been fixed, the temperaturedifference Te which is finally set up in practice at this rate betweenthe fully charged battery and the ambient air is measured. This value Teis adopted as a criterion for the adjustment of the charge. As long asthe temperature difference T from the ambient air does not reach Te, thecharge is allowed to remain at the maximum value permitted by thecharging source. However, as soon as T exceeds Te, the rate of chargewill tloerlreduced until T is again lower than or equal It willtherefore be seen that with a slight delay due to the thermal inertia ofthe battery, the charge will be reduced as soon as the evolution of gascommences.

However, as soon as gassing com Then, with a few oscillations also dueto thermal inertia, this reduction will continue progressively until thebattery is fully charged.

The consequences of this thermal inertia of the battery can be shownwith reference to the preceding example, where the final charging Vrateis 0.035 I, and the initial rate is 0.20 I. Ithas been observed that theevolution of heat at the commencement and at the end of the charging areequivalent. Consequently, untimely operation of the regulator mightoccur duringthe first period. In practice, in order to avoid thisdisadvantage, it is necessary to choose either a slightly lower initialrate (0.1741 for example) orv a higher final rate (0.05 I for example,with a correspondingly higher Te).

It is thus apparent that. it is. expedient to proportion the initialrate permitted by the charging station and the iinal rate allowed for bythe construction of the battery.

The problem ofthe rapid emergency charging of a motor-car startingbattery may be solved as follows:

Initial current 11.(11 capacity in ampere-hours of the batterydischarged Ain hours).

Final current 0.20 I1,the.latter being admissible in this particularcase. because this charge is exceptional and its duration is less. thanone hour.

The method of the invention is extremely safe If one or more damagedelements cause an abnormal temperature increaseinthe first stage of thecharging the current will be reduced, thusv protectingT the battery, andthe incomplete charge resulting therefrom will` act` as'avwarningof. a

fault in the battery.. Similarly if` abatteryis sulphated, the increasein internal resistance will automatically bring aboutthe` charging atthe low rate which is recommended in this case.V

The invention is. also concerned with a device. Y for the automaticperformance of the method hercinbefore described and accordingly thereAis provided apparatus for. charging an accumulator battery having aiirst; casing part in4 contact with the interior ofthe accumulatorbattery, a.,-.s.econd casing. part in thermometric .contact with the.

ambient air and means electricallyresponsive. to a predeterminedtemperature. difference between the two parts, a circuit including, acharging source and the accumulator battery',-means1.for ymodifying saidcircuitto reduce the.. charging current. therein, and .connectionsbetween saidelectrically responsive. means .andv saidv means 4formodifying said circuit whereby the charging cur-- rent is. reduced when.saidV,predetermined1 temperature difference is. exceeded.4

Such a thermometric control-may becontained in anelongated casingsecured-in thecentre `part in place of the plug of anaccumulatorbattery.

The lower part of the casing constitutes a chamber subjected to thetemperature of the battery, while the upper part of the samecasing formsa second chamber maintained at the temperature of the ambientatmosphere.

A regulating device of this particular type wiil4 hereinafter bereferred to as a plug If the device is mounted entirely outside thebattery, the temperature of the latter may be con--` municated to anenclosed chamber by the electric connections of the battery,which'because of the high conductivity of the metals, may be regarded asbeing at a similar temperature to that of the interior of the battery.

The thermometric device may also be employed in conjunction with anyother automatic or nonautomatic charging system which may be providedfor an accumulator battery.

The protection of a battery by an ordinary thermostat is, in fact,illusory. If the thermostat is regulated to a certain value (for example20 C.) above the mean surrounding temperature, and if the externaltemperature rises considerably, the thermostat will operateunnecessarily, without any overload occurring, and will prevent thenormal charging from taking place. In order to avoid this, thethermostat must be set for example at 20 C. above the highest ambienttemperature to which the battery can be subjected.

In cold weatherthis operating temperature of the thermostat will neverbe reached, regardless of thecverload to which the battery is subjected.However a large overload, even at a low temperature, is always harmful,causing disintegration of the active substances, whilst the temperatureincrease aggravates the phenomenon.

In consequence, an ordinary thermostat only gives a restrictedprotection against a large overload, i. e. when there is a high ambienttemperaf ture.

On the other hand, a thermoinetric. device, operating in. directrelation to the external ternperature gives complete safety, as it canbeset for a point only slightly above the ambient temperature, and willoperate as soon as a noticeable overload begins to` cause heating of thebattery.

For a. better understanding of the invention,

two examples of methods and apparatus which;

Figure 3 is a section through another type of.

plug.,

Figure 4 shows diagrammatically a continu.-

ously regulated charging installation incorporate.

ing the plug according. to Figure 3.

Figure. 5 shows the. charging curve of a,discontinuously regulatedbattery, and

Figuren shows the charging curve of' a continuously regulatedv battery.

Referring now to Figure l, the centre part ,of

the plug .is screwedv in place. of. the plugcfI a battery, on theV coverl0.. of the latter. The. plug upper part il is surrounded bythe ambientat-` mosphere, whilstthe lowerpart !2.is brought tothe internal`temperature of thebattery. actual regulator is constituted bytwoheatwsensitive capsules Island lll. disposed at thetopand4 at thebottom of the chambers H 4and i2' respectively and maintained` in. theirhousings byv light springs i5 and I6.v Thev diiierence between thedisplacements or" thecapsules-actson electric contact I2!V through anvarticuiatedlever l'i; rate` The equilibrium temperature ior a lofoperation can vary from one battery to the other according to themanner in whichv it: i. arranged, according to. the` box in w ich itcontained andY according to the Ventilating an rangement.v It istherefore necessary to be able toV adjustv the point of operation ofthe-thermes metric control. For-this purpose, the capsule i3 bearsagainst a displaceable stop l@ cn the flexible wall 20 oi' theapparatus.. This wallv mastitself be deformed by the action of' thescrew?.

which is tightened to. regulate` threaded cap 2l, the position of thestop I9.

The

The regulator of the type hereinbefore described may be used forautomatically charging an accumulator battery B, with discontinuousregulation, by means of the arrangement shown in Figure 2. The battery Bis connected by the charging connector (F1, F2, F3) to a two-stagecharging dynamo, with excitation E and a resistance SIF in series withsaid excitation E.

This resistance may be short-circuited by the relay R, which is in turncontrolled by the contacter lil of the thermometric control.

Under these conditions, the charging of the battery B will be effectedwith discontinuous regulation such as is exemplified by the graph inFigure 5. The charging source only has two fixed rates of operation, onehigh at a charging current IM, corresponding to the maximum power, andone low corresponding to the nal charging current Im. As long as noevolution of gas occurs, the current will remain constant and have thevalue IM. At the end of the charging, the current will be also constantand equal to the nal charging value Im. However, during the intermediateperiod, a succession of high and low rates will occur, the high chargingperiod becoming progressively shorter, whilst the low charging periodsbecome progressively longer, in accordance with the successive openingsand ciosings of the contactor It of plug H-l2. The mean current Iaresulting therefrom, will progressively decrease as shown by the chaincurve.

Figure 3 shows another form of construction of the temperatureresponsive plug, wherein there is an assembly of four resistances 2l,22, 23, 24 connected in the form oi a Wheatstone bridge. rihe twoopposite resistances 23 and E@ are arranged in the lower part of theplug and are subjected to the internal temperature of the battery, whilethe other two resistances 2i and 22 are in the upper part and aresubjected to the ambient temperature. Since the bridge is fed at 25, 2Efrom a suitable source, the current set up in the central branch 2l willbe proportional to the temperature difference and may be used afterampliiication to effect the continuous regulation of the chargingsource.

A corresponding arrangement for automatically charging a battery B isshown in Figure 4. The charging source is in this case connected to analternating current supply with a feed transformer 'I and an assembly ofrectifier cells C R, with continuous adjustment by means of a saturatedinductance S. The continuous saturation current is produced by anampliiier A of any type fed with alternating current, for example, andcontrolled by the bridge W of the resistances of the plug of Figure 3.

In the case of a charging source of this type, owing to the thermalinertia of the battery and the inertia of the control system, thecurrent strength during the period of transition or second chargingstage will comprise damped oscillations around the mean current Ia, asrepresented by the graph of Figure 6.

I claim:

l. A method of automatically charging an accumulator battery in twostages, the rst stage being at constant current and the second stage atvariable current, the iirst stage comprising the step of charging thebattery from a constant current charging source until the temperaturedifference T between the interior of the battery and the ambient air ismore than the temperature diierence Te which is set up when thefullycharged battery is overcharged at the final rate of charging, andsaid second stage comprising the stepsof reducing thecharging currentuntil the temperature difference 'I' does not exceed Te and maintainingthis temperature difference until the battery is fully charged.

2. A method as claimed in claim l, wherein the temperature difference 'Idoes not stand higher than Te during the second charging stage, bydiscontinuous Variation of the charging current, there being a series ofcharging periods at the rate of charging of the first charging stagealternating with a series of charging periods at the nal rate ofcharging.

3. A method as claimed in claim l, wherein the temperature diierence Tdoes not stand higher than Te during the second charging stage by acontinuousy variation of the charging current, there being dampedoscillations on either side of a curve of decreasing mean values.

4. Apparatus for charging an accumulator battery having a rst casingpart in contact with the interior of the accumulator battery, a secondcasing part in thermcmetric contact with the ambient air and meanselectrically responsive to a predetermined temperature differencebetween the two parts, a circuit including a charging source and theaccumulator battery, means for modifying said circuit to reduce thecharging current` therein, and connections between said electricallyresponsive means and said means for modifying said circuit whereby thecharging current is reduced when said predetermined temperaturedifference is exceeded.

5. In apparatus for the automatic charging of storage batteries, asource of charging current, output variation means for controlling theoutput current of said source, a thermo-responsive device responsive tothe difference between the temperature of the interior of a battery andthe ambient atmosphere, actuating means connected between saidthermo-responsive device and said output variation means whereby saidthermoresponsive means causes actuation of said output Variation means,said device and said means being so arranged that the output chargingcurrent of said source is reduced when the said temperature diiierenceto which said thermoresponsive device is responsive, exceeds adetermined critical value.

6. Apparatus according to claim 5, said thermo-responsive device being ahollow elongated plug adapted to be partially inserted in a battery, aiirst temperature expansible capsule located within said plug near theend thereof outside the battery, a second temperature expansible capsulelocated within said plug near the end thereof inside the battery, anelectric switch within said plug, and mechanical control means connectedmechanicallybetween said capsules and adapted to actuate said switch,said actuating means being connected between the contacts of said switchand said output variation means.

7. Apparatus according to claim 5, said source being a generator havinga eld winding and an auxiliary winding in series with said fieldwinding, said output variation means being an electromagnetic circuitbreaker having its contacts connected to shunt said auxiliary winding,said thermo-responsive device being a hollow elongated plug adapted tobe inserted in a battery, a iirst temperature expansible capsule locatedwithin said plug near the end thereof outside the battery, a secondtemperature expansible capsule located within said plug near the endthereof inside the battery, an electric switch within said plug,mechanical control means connected mechanically between said capsulesand adapted to actuate said switch, ysaid actuating means beingconnected between the contacts of, said swite'n and the actuatingWindingcof said electro magnetic circuit breaker.

8. Apparatus according to claim 5, said thermo-responsive device being ahollow elongated plug adapted to be partially inserted in a battery, arst pair of resistance elements Whose resistance varies with temperature1ocated Within said plug near the end thereof outside tlfie battery, asecond pair of resistance elements Whose resistance Varies withtemperature located within said plug near the end thereof inside thebattery, said resistance elements being connected as a bridge with theelements of a said pair forming opposite arms of said bridge, theopposite supply corners of said bridge being connected to said source,and'said actuating means being a connection to said output variationmeans from the other two opposite output corners of said bridge.

JEAN PIERRE GUELPA.

References Cited in the le of this patent UNITED STATES PATENTS NumberNumber Name Date Heyer May 27, 1947 Strawmyer et a1. June 5, 1923Strawmyer Oct. 12, 1926 Rose et a1. Dec. 4, 1934 West Dec. 3, 1935Wasson Jan. 19, 1937 Adams Jan. 26, 1937 Wagar Dec. 14, 1937 WaddellApr. 16, 1940 Kelly Jan 5, 1943 Little et al. Dec. 2, 1947 Little et al.Feb. 28, 1950 Leupold July 11, 1950 Medlar Oct. 17, 1950 Godshalk et a1Feb. 12, 1952 FOREIGN PATENTS Country Date Great Britain Sept. 12, 1929Great Britain Jan. 28, 1931 Great Britain Nov. l, 1937 France June 27,1938

